<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- 检测是否是2到4位汉字 -->
    <script>
    let str1 = "我爱学习"
    let str2 = "我"
    let str3 = "爱学习"
    let reg = /^[\u4e00-\u9fa5]{2,4}$/
    console.log(reg.test(str1))
    console.log(reg.test(str2))
    console.log(reg.test(str3))
    </script>
</body>
</html>